1. Field of the Invention
The present invention relates to an optical card recording/reproducing apparatus which accesses an optical card having an optical data recording section, for data recording into and/or data readout from the card.
2. Description of the Related Art
Although, like an optical disk, such an optical card is not rewritable, it has as a large memory capacity as, for example, 1 to 2 MB, which is several thousands to a million times greater than that of a magnetic card. Therefore, optical cards have wide applications, such as for bankbooks, portable maps and prepaid cards for use in shopping.
A recording/reproducing apparatus for accessing such optical cards is disclosed in Japanese Patent Application No. 61-178876 (corresponding to Japanese Patent Disclosure No. 63-37876), assigned to the same assignee as the present invention.
FIG. 1 is a plan view illustrating an optical card for use in the above apparatus. An optical card 11 has its one surface provided with an optical data recording section 13, which is divided into a plurality of parallel tracks 12 in the lengthwise direction of the card. Movement of optical card 11 with respect to a fixed optical head or movement of a movable optical head with respect to optical card 11 when it is of a fixed type causes tracks 12 to be scanned with a laser beam for data recording/reproducing.
Each track 12 has its center portion serving as a data section 15, and two identifier (ID) sections 14a and 14b, on which the address of the track is recorded, are provided adjacent to both ends of the data section 15, respectively. These ID sections 14a and 14b permit address readout in both lateral movements of card 11 with respect to the optical head. In order to prevent an error in data readout due to a scratch, stain or the like at the edge portions of optical card 11 and sufficiently stabilize the moving speed of the card 11 with respect to the optical head, ID sections 14a and 14b are located at a given distance from the card's edge portions.
FIG. 2 is a block diagram of an apparatus for recording/reproducing data using the optical card disclosed in the aforementioned Japanese Patent Disclosure No. 63-37876. According to this apparatus, a fixed optical head 21 scans a track with a laser beam while moving optical card 11 in the track direction so as to access data section 15 for data recording/reproducing. When the recording/reproducing of one track is completed, optical head 21 moves in the direction perpendicular to the tracks to be ready for recording/reproducing of the next track.
A shuttle 24 is provided at a predetermined location on an endless conveyor belt 23 stretched over pulleys 22a and 22b. Optical card 11 is loaded in shuttle 24 with the card's lengthwise direction coinciding with the moving direction of the shuttle 24.
Accordingly, when conveyor belt 23 is driven, optical card 11 is moved in its lengthwise direction. The belt 23 is driven by a motor 26 coupled to pulley 22a. When shuttle 24 is conveyed by a distance corresponding to the length of the card, motor 26 is rotated in the reverse direction.
Motor 26 is provided with a rotary encoder 27 for detecting the amount and direction of its rotation, and the detection signal from this rotary encoder 27 is fed back to a motor-servo circuit 26.
Optical head 21, which is located at a predetermined location above the path of shuttle 24 conveyed by belt 23, comprises a laser diode 21a, a half prism 21b, a detector 21c, an objective 21d and a lens actuator 21e. A laser beam from laser diode 21a is irradiated onto optical card 11 loaded in shuttle 24, through half prism 21b and objective 21d. Therefore, optical card 11 loaded in shuttle 24 is reciprocated about the laser beam irradiation point. The laser beam reflected at optical card 11 has the direction of its optical path changed 90.degree. by half prism 21b and enters detector 21c.
The output of detector 21c is supplied through a demodulator 29 to a controller 28 as reproduction data. Recorded data is modulated in a predetermined system using a self clock, and the demodulation system of demodulator 29 is associated with the modulation system.
The output of detector 21c is also supplied to focus/track-servo circuit 30, which drives lens actuator 21e in accordance with a command from controller 28 to control the focusing and tracking of objective 21d so that a laser beam is irradiated on the optical card always in a focused state.
Controller 28 controls laser diode 21a through a laser driver 31 to emit a laser beam whose intensity is modulated according to the level, "0" or "1," of recording data at the time of data recording and emit a laser beam with a constant level (normally, "0" level in the data recording) at the time of data reproducing. Controller 28 also controls motor-servo circuit 25, demodulator 29 and focus/track-servo circuit 30 to seek a desired track based on the track data demodulated by demodulator 29.
In response to a command from controller 28, motor servo circuit 25 controls motor 26 based on the detection signal from rotary encoder 27 so that ID sections 14a and 14b and data section 15 of optical card 11 pass the beam irradiation point at a constant speed. This constant speed with respect to the laser beam at the time of data recording/reproducing is required due to the employment of the modulation system using the self clock.
FIG. 3 is a block diagram illustrating the arrangement of a motor-servo circuit 25. This motor-servo circuit 25 comprises a read only memory (ROM) 25a, a digital to analog (D/A) converter 25b a power amplifier 25c, a direction discriminator 25d, an up/down counter 25e, a frequency to voltage (F/V) converter 25f and a subtractor 25g.
ROM 25a has addresses which correspond to the individual points within the reciprocating range of card 11, and has target data of the conveying speed of shuttle 24 at those points stored at the respective addresses. Shuttle 24, before the start of the operation, is secured to its initial position, for example, one edge of shuttle 24 is at the beam irradiation point. Therefore, ROM 25a contains data which gradually accelerates shuttle 24 as the shuttle moves, sets shuttle 24 at a constant speed when the head of ID section 14a reaches the beam irradiation point, and gradually decelerates shuttle 24 when the end of ID section 14b passes the beam irradiation point.
When control signals, such as a drive direction signal DIRC and drive signal DRIV, from controller 28 are supplied to ROM 25a, the address corresponding to the aforementioned initial position is set in ROM 25a.
The speed target data read out from ROM 25a is supplied to motor 26 through D/A converter 25b, subtractor 25g and power amplifier 25c. Subtractor 25g is also supplied with a signal from rotary encoder 27 in order to provide a feedback control to set the rotational speed of motor 26 at the target level.
The output of D/A converter 25b is supplied to a +terminal of subtractor 25g. Rotary encoder 27, which is coupled directly to the shaft of motor 26, outputs a phase A pulse signal and a phase B pulse signal, the order in which these pulses are generated is reversed depending on the rotational directions of motor 26 and which are supplied to direction discriminator 25d. Based on which one of the phases of the phase A and phase B signals is leading, direction discriminator 25d discriminates the moving direction of shuttle 24.
Direction discriminator 25d affixes a plus or minus signal in accordance with the discriminated shuttle moving direction to either one of the phase A and B signals, and sends the resultant signal to F/V converter 25f where it is converted to a voltage signal corresponding to the conveying speed with the direction considered. This voltage signal is then supplied to - terminal of subtractor 25g.
Direction discriminator sends the above-mentioned one of the phase A and B signals to an up count terminal or a down count terminal of up/down counter 25e in accordance with the discriminated shuttle moving direction. Consequently, the count value of up/down counter 25e is increased or decreased by the amount corresponding to the amount of rotation of motor 26. Accordingly, the address of ROM 25a is updated to be always correspond to the current position of shuttle 24 as measured from the initial position.
With the above design, shuttle 24 is gradually accelerated from the initial position, and is moved at a constant speed from the point where the head of ID section 14a reaches the beam irradiation point to a point where the end of ID section 14b passes the beam irradiation point, and is thereafter gradually decelerated to stop moving when it reaches pulley 22b.
In the above recording/reproducing apparatus, when the modulation system at the time of recording uses a self clock, for example, in the case of the modified frequency modulation (MFM) system or 2-7 modulation system, the relative moving speed of the optical card and the laser beam should be constant between ID sections 14a and 14b.
With the above arrangement, however, optical card 11 reciprocates in a state loaded in shuttle 24 secured to conveyor belt 23, so that rotary encoder 27 detects the positional relationship between shuttle 24 and optical head 21, not the positional relationship between optical card 11 and optical head 21.
Since motor 26 is controlled based on the position of shuttle 24, if the position of optical card 11, when loaded in shuttle 24, is shifted in the track direction, or the position of ID sections 14a and 14b in card 11 is shifted due to the error in manufacturing, parts of ID sections 14a and 14b, and data section 15 at the worst, become the acceleration and deceleration regions, thus resulting in inaccurate data recording/reproducing/
A conventional solution to this problem is to provide a greater constant moving range (distance) for shuttle 24 in order to allow for the deviation of optical card 11 which may be caused when it is loaded in the shuttle or when it is manufactured.
However, this measure needs a longer time for reciprocating the shuttle 24, thus lengthening the access time.